New particles comprising a tetracycline or one of its pharmaceutically acceptable salts and an antioxidant, formulations comprising the same and their use in the treatment of infectious diseases are disclosed. Methods of encapsulation of a tetracycline or one of its pharmaceutically acceptable salts and an antioxidant are also disclosed. Formulation of particles contg. doxycycline hyclate and minocycline hydrochloride was disclosed.